Abrasive products formed of a solid or foamed organic polymeric matrix having abrasive granules dispersed throughout and bonded therein are well known and widely used. Typically, the polymeric matrix is composed of either a hard thermoset resin, such as base catalyzed phenol formaldehyde, or a resilient elastomeric resin, such as a polyurethane.
The hard thermosetting resins generally have a high tensile strength and a low elongation at failure, and produce bonded abrasive products which are resistant to significant change when subject to elevated temperatures. However, these hard thermoset resin bonded abrasive products are susceptible to brittle fracture and have the disadvantage of leaving "chatter" marks on the workpiece, particularly when used in off-hand operations.
The elastomeric resins generally produce an abrasive product having some degree of flexibility and resiliency. Typically, these articles provide a smoother abrasive action and a finer surface finish than a hard thermoset resin bonded article. Because of this, flexible elastomeric resin bonded abrasive articles have found a broad range of industrial applications such as in the metal-working and wood-working industries for deburring, finishing and sanding. Unfortunately, however, these elastomeric resin bonded articles often show significant softening at elevated temperatures as might be encountered when an abrasive product is urged against a workpiece at high surface speeds and/or high pressures. Such softening often results in the premature loss of abrasive particles, the undesirable smearing or transfer of portions of the abrasive article to the surface of the workpiece in the case of metal-working applications, or the glazing over of the article's surface in the case of wood-working applications.
Conventional elastomeric resin bonded abrasive articles typically use an elastomeric polyurethane as the binder matrix. The polyurethane binder matrix may be a foam as disclosed in U.S. Pat. Nos. 4,613,345, 4,459,779, 2,972,527, 3,850,589 and U.K. Patent Specification No. 1,245,373, published Sept. 8, 1971, or the polyurethane binder may be solid as disclosed in U.S. Pat. Nos. 3,982,359, 4,049,396 and 4,221,572. Furthermore, the polyurethane binder matrix may be formed of a linear or crosslinked polymer network.
Linear or lightly crosslinked polyurethane networks tend to be more flexible and resilient but have a greater propensity for smearing or glazing. Highly crosslinked polyurethane networks have a reduced propensity for smearing or glazing but typically are too hard and brittle to be useful as a binder for flexible abrasive products. Furthermore, conventional attempts to form a resilient yet smear-resistant binder by introducing a moderate amount of crosslinking into the polyurethane network with standard crosslinking techniques using polyfunctional isocyanates and polyfunctional polyols have proven unsuccessful. Due to the extended distances between crosslinks, the amount of crosslinking necessary to provide smear-resistance by these standard crosslinking techniques typically makes the resin hard and brittle.
An unmet need thus exists for a flexible molded abrasive article that will not smear or glaze when used at high surface speeds and/or high operating pressures.